Learning does not end when practice stops. Memories continue to change after encoding, and sleep is one important environment in which this consolidation occurs.

Replay

Neural activity patterns associated with recent experience can recur during later rest and sleep. In the hippocampus, compressed replay is strongly associated with sharp-wave ripples, especially during NREM sleep.

A leading model is that coordinated slow oscillations, sleep spindles, and hippocampal ripples help reorganize newly encoded hippocampal memories into more distributed cortical representations.

But avoid the oversimplification that "sleep copies files from hippocampus to cortex." Replay also occurs during waking rest, and the exact direction/mechanism of hippocampal-cortical interaction remains an active research area.

Practical implication

Sleep after learning can improve stabilization, integration, and later retrieval. Cutting sleep is therefore not simply losing study time's opposite -- it can interfere with the biological processing of what was already learned.

A useful mental model:

practice creates the trace; offline periods, including sleep, help stabilize and reorganize it.